FIG. 1 schematically shows a structure of an AMOLED (Active Matrix Organic Light Emitting Diode) pixel circuit in the prior art. The pixel circuit comprises a switching thin film transistor T11, a driving thin film transistor T12, a controlling thin film transistor T13, a storage capacitor C14, and an organic light emitting diode OLED15. A gate of the switching thin film transistor T11 is configured to input a scanning signal, a source thereof is configured to input a data signal, and a drain thereof is connected to a gate of the driving thin film transistor T12. A source of the driving thin film transistor T12 is configured to input a first driving voltage OVDD, and a drain thereof is connected to a drain of the controlling thin film transistor T13 and an anode of the organic light emitting diode OLED15. A gate of the controlling thin film transistor T13 is configured to input a control signal SEN, and a source thereof is configured to input an enable signal VCM_en. A first end of the storage capacitor C14 is connected to the gate of the driving thin film transistor T12, and a second end thereof is connected to the drain of the driving thin film transistor T12. A cathode of the organic light emitting diode OLED15 is connected to a second driving voltage OVSS.
As to the pixel circuit as shown in FIG. 1, brightness uniformity of a display panel can be improved by compensating differences in threshold voltage Vth between the gate of the driving thin film transistor T12 and the drain thereof, as well as in current-to-voltage conversion factor k of the driving thin film transistor T12 in each of the pixel circuits. However, differences in luminous efficiency η of the organic light emitting diode OLED15 can also cause non-uniform brightness of the display panel. In an existing pixel circuit, differences in k and in Vth can be compensated, but differences in luminous efficiency η of the organic light emitting diode OLED15 cannot be compensated.